[time-nuts] More recent information on BG7TBL GPSDO?

John Laur johnlaur at gmail.com
Tue Apr 28 14:57:21 EDT 2015

Hello all. Long time listener; first time caller.

I picked up one of the BG7TBL GPSDO units from Ebay, and I am still waiting
for it to arrive. I understand it has its flaws, but my needs are fairly
simple, and I think it will serve.

My intent is to use it as a reference which is better than the 0.1ppm TCXO
in my HF radio, an ANAN-100D (HPSDR architecture); I would like a PPS
reference so that I can experiment with timestamped IQ samples; and I would
like to build an NTP server using a BeagleBone Black. I think this will
serve to do these things even if it is not the ideal equipment.

I have read I believe all of the previous discussion on this list over the
past few months including the excellent study by John KE5FX, and I had a
few questions to see if there had been any new developments. I understand
some may have communicated with the designer as well.

Does anyone else have further information on the serial interface? Is the
NMEA data directly to/from the U-Blox module or does the internal firmware
filter/augment it to allow monitoring or tuning of other internal
parameters - for instance can one set cable delay? What is its suitability
for running as a GPS/PPS reference for an NTP server? Any other software
suggestions for keeping an eye on it?

Second, has the small frequency error identified by John been corrected, or
is it a problem endemic to the design (I think maybe this was identified as
a resolution limit of the DAC providing OCXO control voltage; could it be

As this is my first moderately accurate device in the shack, is my best
approach just to put it on the shelf, leave it on for a long time, and
trust it? I can see how its easy to begin the slide when there is only one
clock to stare at skeptically.

John Laur

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